Combustion turbines comprise a casing or cylinder for housing a compressor section, combustion section and turbine section. The compressor section comprises an inlet end and a discharge end. The combustion section or combustor comprises an inlet end and a combustor transition. The combustor transition is proximate the discharge end of the combustion section and comprises a wall which defines a flow channel which directs the working fluid into the turbine section's inlet end. A supply of air is compressed in the compressor section and directed into the combustion section. Fuel enters the combustion section by means of a nozzle. The compressed air enters the combustion inlet and is mixed with the fuel. The air/fuel mixture is then combusted to produce high temperature and high pressure gas. This working gas is then ejected past the combustor transition and injected into the turbine section to run the turbine.
The turbine section comprises rows of vanes which direct the working gas to the airfoil portions of the turbine blades. The working gas flows through the turbine section causing the turbine blades to rotate, thereby turning the rotor, which is connected to a generator for producing electricity.
As those skilled in the art are aware, the maximum power output of a combustion turbine is achieved by heating the gas flowing through the combustion section to as high a temperature as is feasible. The hot gas, however, heats the various turbine components, such as the transition, vanes and ring segments, that it passes when flowing through the turbine.
Accordingly, the ability to increase the combustion firing temperature is limited by the ability of the turbine components to withstand increased temperatures. Consequently, various cooling methods have been developed to cool turbine hot parts. These methods include open-loop air cooling techniques and closed-loop cooling systems.
Conventional open-loop air cooling techniques divert air from the compressor to the combustor transition to cool the turbine hot parts. The cooling fluid extracts heat from the turbine components and then transfers into the inner transition flow channel and merges with the working fluid flowing into the turbine section. One drawback to open-loop cooling systems is that it diverts much needed air from the compressor, e.g., a significant amount of air flow is needed to keep the flame temperature of the combustor low. Another drawback to open-loop cooling of a combustor transition is increased No.sub.x emissions. It is, therefore, desirable to provide a cooling system that diverts less air from the compressor and controls No.sub.x emissions.
Conventional turbine closed-loop cooling assemblies generally comprise at least one manifold, strain relief devices, such as piston rings or bellows, and a supply of cooling fluid located outside the turbine. The manifold typically comprises an outer casing. The strain relief devices are employed to connect the manifold outer casing proximate the component that must be cooled.
The closed-loop cooling manifolds receive cooling fluid from the source outside the turbine and distribute the cooling fluid circumferentially about the turbine casing. Unlike open-loop cooling systems, the closed-loop cooling fluid remains separated from the working fluid that flows through the turbine flow path and is diverted to a location outside the turbine.
Conventional closed-loop cooling systems, however, employ relatively complex manifold attachment assemblies. These manifold attachment assemblies, in turn, add to the overall expense of maintaining a combustion turbine. Conventional manifold attachment assemblies must be precisely designed to enable the manifolds to sufficiently couple with the turbine casing. It is, therefore, desirable to provide a more simplified and economical closed-loop cooling scheme.
Conventional closed-loop cooling schemes typically utilize complex piping schemes to connect a manifold to the cooling fluid source outside the turbine. When cooling several hot parts of a turbine, the number of pipes can be great. Each pipe also requires joints such as piston rings or bellows for attachment to the manifold, or if there is no manifold, directly to the turbine hot parts. More pipes and joints yield more costly installation and maintenance of the turbine. It is, therefore, desirable to provide a closed-loop cooling scheme that requires less pipes and therefore, less joints, than conventional cooling schemes.
Piston rings and bellows of conventional closed-loop cooling schemes also have their own drawbacks. Both piston rings and bellows have poor fatigue life characteristics. Piston rings have significant leakage rates, require large pressure drops to operate properly and must maintain proper alignment to be effective. Both bellows and piston rings are also difficult to install as well as maintain. In addition, bellows and piston rings are not very flexible in responding to changing conditions or positioning of parts to which they connect. It is, therefore, desirable to provide a closed-loop cooling scheme that utilizes pipe joints that are superior to piston rings and bellows.